Stringent requirements as to leaktightness are imposed on many systems and products in industry and research. It depends on the type of leak, leak rate or the size of the leak which leak searching method is applied, respectively, which leak indicator is employed.
In the instance of units under test or subassemblies manufactured in the refrigerants, automotive or other industries, the method of sniffer leak detection is frequently employed. This requires, that there be present in the unit under test or subassembly a test gas, preferably at an overpressure. Frequently helium is employed as the test gas, which is introduced before sealing into the hollow spaces which are to be analysed for the presence of leaks. It is also known to employ gases present anyway in the units under test or subassemblies as the test gas, for example SF6 or halogen gases in the refrigerants industry.
The unit under test which is to be analysed for the presence of leaks is scanned with the aid of the intake point (tip) of a sniffer gun, whereby said tip accepts the test gas escaping from a possibly present leak and supplies it to a test gas detector. This test gas detector may be accommodated together with other components within an instrument to which the sniffer gun is linked, among other things, through a hose. If the detector is sufficiently small (for example, an infrared gas analyser) then it also may be accommodated in the gun itself, thereby significantly reducing the response time.
Test gas leak indicators need to be calibrated frequently. To this end it is known to employ test leaks exhibiting a defined leakage. Test leaks for these purposes comprise a gas reservoir and a constriction of known conductance. To calibrate a leak indicator with a sniffer gun, the sniffer tip is brought in to the vicinity of the constriction, and the leak rate indication is adjusted.
Test leaks should exhibit, over a time which is as long as possible (significantly over one year), a constant gas flow and should be, moreover, so small that they can be accommodated within the housing of a leak indicator. This requires that the test gas be present in the test leak at a high pressure (8 bar and more). Test leaks of this kind are temperature sensitive. This applies in particular when the test gas is in the liquid state at the pressures stated. For safety reasons, a maximum temperature must not be exceeded. Installing a test leak of this kind within a leak indicator in which heat generating components are present, causes problems.